"Perplexed in Peoria" sbcglobal.net> wrote in news:e87nvg$2dlp
$1@darwin.ediacara.org:

This is old news. The Just So Story is that rather than competing with
older male siblings for resources for children, it is more advantageous to
help the children of older siblings (a kin selection effect). Another
explanation is that a gene that predisposes male children to be homosexual
also leads women who carry it to have more children, thus offsetting the
lesser reproductive success of homosexual male children. The birth order
effect in this latter scenario is due to stochastic rather than selected
factors.

Yours,

Bill Morse

"William Morse" twcny.rr.com> wrote in message news:e8sqn8$2img$1@darwin.ediacara.org...

Well, what is claimed to be new is the showing that the effect shows up
even in males reared apart from their older maternal half-brothers. So,
it likely is womb-mediated.